This invention relates to an antenna unit for receiving satellite signals transmitted from artificial satellite and, in particular, relates to a shield cover used in the antenna unit and a method of fabricating an antenna module.
Various antenna units for receiving satellite signals transmitted from artificial satellites have been proposed. For example, such antenna units include a Global Positioning System (GPS) antenna unit for receiving GPS signals transmitted from GPS satellites and a Satellite Digital Audio Radio Service (SDARS) antenna unit for receiving SDARS signals transmitted from SDARS satellites.
For instance, in recent years, the so-called global positioning system has been spreading in which a receiver receives signal waves transmitted respectively from a plurality of artificial satellites orbiting the earth and the current position of the receiver itself is detected based on information included in the received signal waves. This system is generally called a GPS (Global Positioning System) in those countries such as Japan and USA. The GPS generally uses GPS satellites controlled by the US Department of Defense. As similar systems, there are “GALILEO” used in Europe and “GLONASS” used in Russia. Herein, a positioning system using artificial satellites, the artificial satellites used in the positioning system, signal waves transmitted from the artificial satellites, receivers for receiving the signal waves, and so on are referred to as a GPS, GPS satellites, GPS signals, GPS receivers, and so on, respectively, for convenience sake.
The GPS is capable of detecting a current position of a GPS receiver itself with high accuracy and substantially in real time. Accordingly, the GPS is mainly used such that a GPS receiver is mounted in a moving object such as an automobile, an airplane, or a portable telephone and the current position of the moving object is measured.
Presently, GPS receivers that are suitable when installed in automobiles, i.e. so-called car GPS receivers, are rapidly spreading. When installing the GPS receiver in the automobile, a GPS receiving antenna unit for receiving GPS signals may be almost disposed outside the automobile, for example, on a roof.
On the other hand, the SDARS (Satellite Digital Audio Radio Service) is a radio service according to a digital radio broadcasting using artificial satellites (which will called “SDARS satellites” hereinafter) in the United States of America. That is, in recent years, a digital radio receiver, which receives the satellite wave from the SDARS satellites or the terrestrial wave so as to listen to the digital radio broadcasting, has been developed and is put to practical use in the United States of America. Specifically, two broadcasting stations called XM and Sirius provide radio programs on 250 or more channels in total. The digital radio receiver is generally mounted on a mobile object such as an automobile and is adapted to receive a radio wave having a frequency of about 2.3 gigahertz (GHz) as a received wave to listen to the digital radio broadcasting. In other words, the digital radio receiver is a radio receiver capable of listening to mobile broadcasting. Inasmuch as the received wave has the frequency of about 2.3 GHz, a reception wavelength (resonance frequency) λ thereof is equal to about 128.3 mm. It is noted here that the terrestrial wave is a radio wave obtained by receiving the satellite wave at a ground station, slightly shifting the frequency of the satellite wave, and retransmitting the linear polarized wave. Thus, the terrestrial wave is the linear polarized wave exhibiting linear polarization while the satellite wave is a circular polarized wave exhibiting circular polarization.
An XM satellite radio antenna apparatus normally serves to receive circular polarized radio waves from two stationary satellites and, in an insensitive zone of the circular polarized waves, receives a radio wave by using a terrestrial linear polarization portion of the radio antenna apparatus. On the other hand, a Sirius satellite radio antenna apparatus normally serves to receive circular polarized radio waves from three orbiting satellites (synchronous type) and, in the insensitive zone, receives a radio wave by a terrestrial linear polarization portion of the radio antenna apparatus.
As described above, the radio wave having the frequency of about 2.3 GHz is used in the digital radio broadcasting. Therefore, an antenna for receiving the radio wave may be almost located outside as known in the art. If the digital radio receiver is mounted in the mobile object such as the automobile, the antenna unit may be almost attached to a roof of the mobile object (car body).
Such various antenna units for receiving satellite signals transmitted from artificial satellites have been proposed. For example, an antenna unit capable of easily positioning a packing member to a top cover is disclosed in Japanese Unexamined Patent Publication Tokkai No. 2006-237917, namely, JP 2006-237917 A which is called Patent Document 1 hereinafter. An easy-to-assemble antenna unit is disclosed in U.S. Pat. No. 7,339,538 issued to Akira Yoneya et al. that will be called Patent Document 2 hereinafter. Furthermore, an antenna unit capable of improving a waterproofing function is disclosed in Japanese Unexamined Patent Publication Tokkai No. 2006-237951, namely, JP 2006-237951 A which is called Patent Document 3 hereinafter.
In addition, a shield cover used in an antenna unit is disclosed in U.S. Pat. No. 7,327,328 issued to Akira Yoneya et al. that will be called Patent Document 4 hereinafter. The shield cover is mounted on a rear surface of a circuit board by manually soldering by means of an soldering iron. As a result, there is a problem where a process of solder-fixing becomes longer and the number of working increases. In addition, there is another problem where thermal stress for the circuit board increases and quality becomes unstable because the shield cover is manually mounted on the rear surface of the circuit board.
An electronic component enabling efficient fixation of a shield cover to a sheet substrate (a circuit board) is disclosed in U.S. Pat. Application Publication No. 2008/0292846 A1 which will be called Patent Document 5 hereinafter. The shield cover disclosed in the Patent Document 5 is of quadrilateral lid shape and has four peripheral edge sides. In the Patent Document 5, to fix the shield cover to the sheet substrate, solder is not coated on the sheet substrate side, but attached to the shield cover side. Namely, in a transcription table to which creamy solder paste (cream solder) is supplied, the peripheral edge sides of the shield cover are dipped in the state of holding the shield cover by means of a holder (a vacuum nozzle) of an automatic component mounting machine (a mounter) and thereby the cream solder is attached to the peripheral edge sides of the shield cover. In this state, the shield cover is moved and disposed corresponding to a shield pad of the sheet substrate, by means of the automatic component mounting machine (the mounter). Next, the reflow process is performed in a state that the shield cover is placed on the sheet substrate, so as to fix the shield cover to the sheet substrate by soldering.
In the Patent Document 5, the shield cover is held by means of the holder (the vacuum nozzle) of the automatic component mounting machine (the mounter). Accordingly, it is possible to reduce the number of working. However, inasmuch as the shield cover disclosed in the Patent Document 5 is of the quadrilateral lid shape, the weight of the shield cover is cumbersome. As a result, it is necessary to become larger an attraction force of the holder (the attracting nozzle) of the automatic component mounting machine (the mounter). In other words, the automatic component mounting machine (the mounter) becomes upsizing.
A frame of a shield member for shielding by covering a region to be shielded of a circuit board and a method of mounting the shield member are disclosed in Japanese Unexamined Patent Publication Tokkai No. 2006-344814, namely, JP 2006-344814 A which is called Patent Document 6 hereinafter. In the Patent Document 6, the shield member comprises a shield cover and a frame. The frame of the shield member is provided at a standing state to an end edge portion of a region to be shielded of a circuit board and has an upside opening having a marginal frame wall surrounding the region to be shielded. The frame forms the shield member with the shield cover combined with the frame in the form of closing the upside opening. In the upside opening of the frame, a vacuum pad having a nozzle vacuumed surface to be vacuumed to a frame carrying vacuum nozzle is disposed such that it is supported and fixed to the marginal frame wall with beams which extend from a plurality of positions of the marginal frame wall and are formed, respectively. The vacuum pad is disposed above the upper end of the marginal frame wall.
A method of mounting the shield member disclosed in the Patent Document 6 comprises carrying the frame to the region to be shielded of the circuit board in a state where the nozzle vacuumed surface of the vacuum pad of the frame is vacuumed by the frame carrying vacuum nozzle to dispose the frame to the region to be shielded of the circuit board, cutting off the ends of beams at the marginal frame wall from the marginal frame wall to cut the vacuum pad and the beams from the marginal frame wall, and combining the shield cover with the frame in the form of closing the upside opening from which the vacuum pad and the beams have been removed. After the shield cover is combined with the frame, the frame and the shield cover are joint-fixed to the circuit board by means of a conductive connection material such as solder.
In the Patent Document 6, the frame is required in addition to the shield cover. As a result, there is a problem where the number of parts increases. In addition, in the Patent Document 6, after the shield cover is combined with the frame, the frame and the shield cover are joint-fixed to the circuit board by means of the conductive connection material such as solder. As a result, in the manner similar to the above-mentioned Patent Document 4, there are problems where a process of solder-fixing becomes longer and the number of working increases and thermal stress for the circuit board increases and quality becomes unstable.